A uvbyCaHbeta CCD Analysis of the Open Cluster Standard, NGC 752

Abstract

Precision uvbyCaHβ photometry of the nearby old open cluster, NGC 752, is presented. The mosaic of CCD fields covers an area ∼42′ on a side with internal precision at the 0.005 to 0.010 mag level for the majority of stars down to V ∼ 15. The CCD photometry is tied to the standard system using an extensive set of published photoelectric observations adopted as secondary standards within the cluster. Multicolor indices are used to eliminate as nonmembers a large fraction of the low probability proper-motion members near the faint end of the main sequence, while identifying 24 potential dwarf members between V = 15.0 and 16.5, eight of which have been noted before from Vilnius photometry. From 68 highly probable F dwarf members, we derive a reddening estimate of E(b − y) = 0.025 ± 0.003 (E(B − V ) = 0.034 ± 0.004), where the error includes the internal photometric uncertainty and the systematic error arising from the choice of the standard (b−y, Hβ) relation. With reddening fixed, [Fe/H] is derived from the F dwarf members using both m1 and hk, leading to [Fe/H] = -0.071 ± 0.014 (sem) and -0.017 ± 0.008 (sem), respectively. Taking the internal precision and possible systematics in the standard relations into account, [Fe/H] for NGC 752 becomes -0.03 ± 0.02. With the reddening and metallicity defined, we use the Victoria-Regina isochrones on the Str¨omgren system and find an excellent match for (m − M) = 8.30 ± 0.05 and an age of 1.45 ± 0.05 Gyr at the appropriate metallicity.